1. Field of the Invention
The present invention relates to a process for preparing a graft copolymer. More particularly, the present invention relates to a process for preparing a graft copolymer which can be used for preparing bottles for cooling drinks, such as beer and cola; containers for foodstuffs or medicines; and packaging materials, such as for green vegetables, etc.
2. Description of Prior Art
Acrylonitrile polymers possess excellent transparency, but are so poor in molding workability, that it is particularly difficult to melt mold acrylonitrile polymers because of their poor flowability, even at temperatures as high as 250.degree.C. Moreover, acrylonitrile polymers are so poor in impact strength that even when molded, they are quite easily broken.
It has been suggested in the prior art to alleviate these problems by copolymerizing acrylonitrile with other vinyl monomers, such as, for example, styrene, vinyl chloride, methyl acrylate, vinyl acetate, etc., but even when copolymerized according to those prior art suggestions, satisfactory impact strength cannot be obtained. It has also been suggested to copolymerize acrylonitrile with styrene in the presence of a butadiene polymer to form so-caled "ABS resins", but such resin compositions are poor in transparency, even though they are excellent in flowability and impact strength. It has also been suggested to copolymerize an olefinic unsaturated nitrile, such as acrylonitrile, with an olefinic unsaturated carboxylic ester, such as an acrylate ester, in the presence of a nitrile rubber. However, although that expedient does result in improvements in flowability and impact strength, the copolymerization product does not possess satisfactory flowability properties.
It would be desirable to provide a resin composition which possesses a comparable degree of transparency and gas impermeability, as acrylonitrile polymers, yet which has sufficient flowability, so that it can be easily molded by conventional techniques, and whose molded products are high in impact strength, etc. Such a resin composition would be particularly well adapted for use in the formation of bottles and containers, such as for food stuffs, medicines, etc., whereby gases such as oxygen and carbon dioxide would be effectively excluded from the closed container or bottle.